8. The therapeutic effects of cannabinoids

8.6 Cannabinoids as analgesics

There is some animal evidence that THC has an analgesic effect which operates via a different mechanism from that of the opioid drugs (Segal, 1986). There is a small amount of human experimental studies which have reported mixed evidence of an analgesic effect (Nahas, 1984). There has been little clinical evidence beyond historical use for various forms of chronic pain, including migraine, dysmenorrhoea, and neuralgia, and the small number of case histories of its use in chronic pain, dysmenorrhoea, labour pain, and migraine reported by Grinspoon and Bakalar (1993).

Only one double-blind controlled cross-over study has been reported. This study compared the analgesic effect of THC and codeine in patients with cancer pain (Noyes et al, 1975). The findings suggested that 20mg of THC was of equivalent analgesic effect to 120mg of codeine. However, neither drug produced substantial analgesia in these patients, and the majority of patients found the psychotropic effects of 20mg of THC sufficiently aversive that they discontinued its use. Clearly, much more basic pharmacological and animal investigation is required before cannabinoids or their derivatives have any clinical use as analgesics. Nevertheless, such investigations may be worth pursuing because of the dependence potential of the more potent opioid analgesics, and the likelihood that any cannabinoid mediated analgesic effect operates by a different mechanism to that of the opioids.